Generally, in the case where an extrusion material (billet) of a metal, such as aluminum or an alloy thereof is extruded by an extrusion pressing machine, a stem is mounted at the forward end portion of a main ram driven by a hydraulic cylinder, and with the container pressed against a dice, the billet on the billet loader is pressed by the stem at the forward end portion of the main ram and loaded in the billet accommodation unit of the container. By driving the main ram further forward with the hydraulic cylinder, the billet is strongly pressed by the stem. Then, a molded product is extruded from the dice outlet.
In this conventional extrusion pressing machine, the forward end of the stem is required to be retreated by the length of the billet when the billet is loaded in the container, and therefore the stroke of the main ram is equal to the sum of the billet length and the stem length. To secure the stroke of the main ram, the entire length of the conventional extrusion pressing machine is increased, which in turn increases the size of the hydraulic cylinder for driving the main ram. Thus, a greater amount of the working oil is required to operate the machine.
In recent years, a compact extrusion press has been designed. The compactness can save the space occupied arid energy consumed by the extrusion pressing machine. An extrusion pressing machine known as a short stroke press type has been developed as One technique for achieving compactness. In the conventional extrusion pressing machine, the space for supplying the billet is required to load the billet in the container, and the stroke of the main ram is lengthened correspondingly. In view of this, in the pressing machine of a short stroke press-type, the mariner in which the billet is supplied is designed so that the stroke of the main ram is shortened by the length of the billet-supplying space.
According to the short stroke press system, the extrusion pressing machine as a whole can be shortened into a compact form along with the non-extrusion time (idle time). Further, the amount of the working oil of the hydraulic cylinder for driving the main ram can be reduced. As a result, the space occupied and energy consumed by the extrusion pressing machine can be saved.
The short stroke press system can be classified into two types according to the direction in which the billet is supplied with respect to the container. One is the short stroke press system called the front loading type. In this front loading type, the container is moved to the stem side at the time of supplying the billet to secure the billet-supplying space on the side nearer to the dice from the container position after movement. In other words, the billet is supplied between the dice and the forward end of the stem.
In the press system of this front loading type, the billet is supplied by “sandwiched charge”, and therefore since it is important to maintain the center accuracy of the billet loader unit, the maintenance and control of the billet loader unit are required. The accuracy of the diameter, the curve arid the end surface of the billet is also required. Actually, these requirements are met by increasing the inner diameter of the container. The increased inner diameter, however, is a major cause of taking the blister in the product.
The other type that has been developed is the short stroke press system known as a rear loading type as shown in FIG. 3. In this rear loading type, the stem is moved horizontally or upward to secure the billet-supplying space at the time of supplying the billet. From the initial stem position, the stem is moved horizontally or upward to provide the billet-supplying space on the side of or under the stem on the stem side of the container. The billet is supplied into this space. (See Japanese Unexamined Patent Publication No. 4-231110 and Japanese Unexamined Patent Publication No. 8-206727).
FIG. 3 shows an outline of the extrusion pressing machine of rear loading and short stroke press type in a configuration as viewed from above the extrusion pressing machine. In this extrusion pressing machine, an end-platen 1 and a cylinder mount block 2 are fixedly coupled to each other by tie rods 3. The end platen 1 has mounted thereon the dice 4 having a die through which the billet is extruded into a product, and the container 5 having a billet accommodation unit C is pressed against the dice 4.
As shown in FIG. 3, the cylinder mount block 2 has mounted thereon a main hydraulic cylinder 8 to move the stem 6 along the axis of the billet accommodation unit C of the container 5. Though not shown, a main ram driven under oil pressure is arranged in the main hydraulic cylinder 8, and a stem support member 7 is mounted at the forward end of the main ram. The stem 6 is mounted on this stem support member 7, so that when the main ram of the main hydraulic cylinder 8 is driven, the stem 6 is moved along the axis of the billet accommodation unit C of the container 5. Incidentally, a mechanism for moving the stem 6 horizontally or downward at the time of supplying the billet is hot shown in FIG. 3.
An example of the uplift mechanism of the stem used for the extrusion pressing machine of rear loading and short stroke press type described above is shown in FIGS. 4A and 4B. In this case, a stem support base shown in FIG. 4A is configured of a stem uplift support member 71, a slide guide member 72, a stem slide base 73 and a stem clamp member 74. The stem slide guide member 72 is fixed on a vertically movable stem support member 71 and has slide grooves along which the side ends of the stem slide base 73 are slidable vertically.
The base portion of the stem 6 is clamped by the stem clamp member 74 on the stem slide base 73, so that the stem 6 is held and supported horizontally. Further, the stem slide base 73 is vertically moved by the operation of a vertical stem drive hydraulic cylinder 79. Though hot shown, a mechanical stopper is provided to define the lower limit of the stem slide base 73, and the position sensor of the mechanical stopper detects whether the vertical center of the stem 6 has entered a tolerable value or not. FIG. 4A shows the state in which the stem slide base 73 is located at the lower limit, in which the center of the stem 6 is aligned with the axis of the billet accommodation unit C of the container 5.
The billet-supplying operation of the extrusion pressing machine of rear loading type shown in FIG. 5 is explained with reference to FIGS. 5A to 5C. In FIGS. 5A to 5C, the same parts as the extrusion pressing machine shown in FIG. 3 are designated by the same reference numerals, respectively.
First, as shown in FIG. 5A, the stem 6 is moved upward, and the billet B held by the billet loader unit BL is supplied into the space formed under the stem 6 sideways of the extrusion pressing machine at the axial position of the billet accommodation unit C of the container 5. The state in which the stem 6 is moved upward under this condition is shown in FIG. 4B.
In FIG. 4B, the vertical stem drive hydraulic cylinder 79 is activated and the stem slide base 73 is pushed up to a predetermined height from the lower limit position. As the result of the upward movement of the stem slide base 73, the stem 6 clamped to it is also moved up to a predetermined height from the position of axis X. After the stem 6 moves upward, a space is formed at the position on axis X, and the next billet B is pushed out and can be supplied into this space as shown.
Then, as shown in FIG. 5B, me billet insertion unit of the billet loader BL is driven along the axial direction, so that the billet B is inserted and loaded in the billet accommodation unit C of the container 5.
As shown in FIG. 5C, the billet B is further inserted, and when completely loaded in the billet accommodation unit C, the billet loader unit BL is retreated sideways from the extrusion pressing machine and proceeds to hold the next billet. After that, the stem 6 which has been moved up is driven downward and returns to the initial axial position of the billet accommodation unit C. Then, the main hydraulic cylinder 8 is driven and the main ram is advanced, so that the stem 6 begins to press the billet B, after which the extruded billet B is molded by the dice 4.